What We Once Were tells the story of Bree, a 17 year old girl living in a world where most of the population was wiped out due to a virus. Bree desperately tries to avoid the Nox (Noxious), those that have the virus, but that's not Bree's biggest concern though. Bree has special abilities that she can't explain and she must learn how to control them without letting her secret slip or injuring the people she cares about.